An assay for the functional capacity of the folate coenzymes in the body will be developed. This depends on the ability of lymphocytes to convert (14C) formate to inosinic acid. Values for normal individuals have been established; values to folate deficient subjects will be obtained and compared with normals. The major folate binding proteins of liver cytosol will be purified and characterized as to type of folate bound and concentrates bound. Then antibody to the purified binding protein will be prepared and this will be used to identify this protein in other tissues. BIBLIOGRAPHIC REFERENCES: Zamierowski, M. and Wagner, C. "The Characterization of High Molecular Weight Complexes of Folic Acid in Mammalian Tissues". Chemistry and Biology of Pteridenes, Walter de Gruytee, Berlin. 209-217. (1976). Horne, D.W., Briggs, W.T., and Wagner, C. "A Functional, Active Transport System for Methotrexate in Freshly Isolated Hepatocytes." Biochem. Biophys. Res. Comm. 68: 70-76, (l976).